Hello
Which of the following routers are suitable for implementing mangle in terms of processing power? What is the recommended resources( cpu , memory, …)
Rb450
Rb750
Rb951-2n
Mangle means that fast-track is out of question and that severely increases processing load (and thus reduces practical throughput). You did not tell what throughput you require, but none of devices you listed (if those are full model names) is exactly powerful.
Mangle is not really memory-demanding, so you should focus on CPU performance (multi-core helps).